Microbial activity in peat-reduced plant growing media: Identifying influential growing medium constituents and physicochemical properties using fractional factorial design of experiments

Abstract The development of peat-reduced plant growing media for horticulture is needed to tackle sustainability concerns related to the peat production process. Alternative growing media constituents with unique physicochemical properties, like coir pith, wood fiber, compost, and inorganic materials are currently used. However, little is known about the impact of these materials on microbial activity. Because microbial communities play an important role in plant growth and development, the impact of various growing media constituents on microbial activity was analyzed using two-level fractional factorial statistical design of experiments. The results showed that growing media composition greatly affected microbial activity. White peat (+2.4% CO2) and composted bark (+1.5% CO2) significantly promoted microbial activity over black peat and green waste compost respectively. In contrast, the organic materials coir pith and wood fiber, as well as the inorganic materials perlite and sand, had little effect on microbial activity. Physicochemical analysis of the different growing media mixtures revealed that the water-filled porosity (WFP) was the most important parameter driving microbial growth, increasing microbial activity (+2.1% CO2) at 62.95% WFP compared to 82.95% WFP. Our results are instrumental for developing novel organic growing media with distinct microbial features to move towards a low peat sustainable horticulture.